Phase transformation of the monochalcogenides SmX (X S, Se, Te) under high pressure

The high-pressure behaviour of the monochalcogenides of samarium (SmS, SmSe and SmTe) was investigated up to pressures of 55 GPa using the energy dispersive X-ray diffraction technique and synchrotron radiation. SmTe and SmSe show abnormal volume changes around 5 and 7 GPa respectively. SmS shows a phase transformation at low pressure (less than 1.8 GPa), retaining the same cubic structure, but undergoing a considerable volume collapse and a change of colour. SmS and SmSe both exhibit a phase transition from NaCl- to CsCl-type structure at high pressure, which has not been observed previously.